Insulin is classified according to three factors: how long it takes to start working (onset), when it peaks, and how long it lasts (duration). There are two main categories: Background (basal) insulin, which tends to last longer and delivers a steady dose of insulin; and mealtime (bolus) insulin, which tends to have a shorter duration but delivers a greater amount of insulin to handle spikes in blood glucose after mealtimes. Watch to learn more about the different types of insulin.